1. Field of the Invention
This invention relates to the field of flexible manufacturing of parts and more particularly to the field of shaping of parts from fluids which change from a liquid to a solid during a curing phase and still more particularly to the shaping of parts by means of an electric field.
2. Background Information
It is known to construct molds having a volume and an exterior form for retaining a liquid molding compound, to place liquid in these volumes, to allow the liquid to cure and then to remove the form, thereby revealing the article. In order to mold an article in this manner, it is first necessary to have a pattern for the article or a mold made with an interior conforming to the shape of the article. In U.S. Pat. No. 5,194,180, the disclosure of which is hereby incorporated by reference, it is taught that an electroset article can be formed by making a conductive mold having at least two electrode surfaces and that this mold can be used in conjunction with an electroset fluid to accelerate the production of articles. This copending application also teaches electroset materials which are usable in an electroset mold. Electroviscous fluids refer to fluids which exhibit the property of increased viscosity when the fluid is subjected to an electric field. One phenomenon for electrically controlling the viscosity of a fluid is commonly known as the Winslow effect. The term Winslow effect refers to the phenomenon of electrically controlling the viscosity of a fluid comprising a suspension of finely divided electrically polarizable matter in a dielectric fluid by subjecting the fluid to an electric field. Within this disclosure and the appended claims, the finely divided electrically polarizable matter is referred to as aggregate.
Numerous types of electroviscous fluids and aggregates are disclosed in my copending applications referenced above as well as in the prior art. Electroviscous fluids and aggregates for electroviscous fluids are disclosed in the prior art in U.S. Pat. Nos. 4,687,589; 3,427,247; 3,970,573; 3,984,339; 4,502,973; 4,737,886, the disclosures of which are hereby incorporated by reference.
It is known that molded articles can be made by pouring a phase changing vehicle into a form, allowing the vehicle to set or cure and then removing the molded article from the mold. As used herein the term phase changing vehicle applies to any composition which changes state from a flowable to a less flowable or solid state when such compositions cure or set in the normal course of their use. Numerous commercially available compositions are available which exhibit such phase changing characteristics, examples of which are hereinafter disclosed. These include vehicles made from mixing multipart constituents which chemically react and vehicles having a contituent or a composition of constituents which reacts with its surroundings such as for example air.
It has been found that aggregates as are suitable for use as aggregates in electroviscous fluids may be advantageously put to other purposes. When a suitable electroviscous fluid aggregate is added to a phase changing vehicle, an electroviscous fluid is formed whereby the fluid is susceptible of being held in place by the Winslow effect during the time of phase change of the composition. Suprisingly, it has been found that a composition comprising electroviscous fluid aggregate in a phase changing vehicle will, when the composition is subjected to an electric field, set or cure much more rapidly than the same composition sets or cures when not under the influence of an electric field. The phenomenon of accelerated curing of such a composition is referred to as the second Reitz effect.
Within this disclosure and the appended claims, the term electroset composition is used to relate to a composition which is susceptible to being shaped or cured by influence of an applied electric field.
An electroset composition comprises a phase changing vehicle and an electrically polarizable aggregate. The term aggregate is used in the collective to include a multiplicity of polarizable particles. The composition is responsive to an applied electric field in that the field cooperates to hold the material in place while the material cures and to drastically accelerate the cure of the material.
One aggregate as disclosed in my copending application Ser. No. 07/219,522 (now abandoned) was tested and found to be useful for the purposes of the present invention. Thereafter, it was found that aggregates other than those of my copending application were also useful in forming electroset compositions in accordance with the present invention. Consequently it is expected that any of the aggregates disclosed in my copending application as well as any of the aggregates disclosed in the prior art as generally useful for making electroviscous fluids are also generally useful as aggregates for forming electroset compositions. Aggregates suitable for use in an electroset composition include those suitable for use as aggregates for electroviscous fluids.
Preferably the phase changing vehicle has good dielectric properties so that current flow in the electric field is kept to a minimum. Also, it is preferable if the density of the aggregate particles is matched to the density of the phase changing vehicle so that the paticles are maintained uniformly suspended in the composition.
The advantages of the compositions and methods will be readily understood by those skilled in the art in the light of this disclosure. While it is known that many materials may be initially fluid enough to be injected into a mold and permitted to harden into solids, many of these materials have slow cure times, that is, they do not harden rapidly into an identifiable and transportable form. On the other hand, an electroset composition can be cast into a mold and held in place and cured by the application of an electric field.
Another advantage is that the materials of the invention may have their cure rate electrically determined, accelerating the cure with a high potential, low energy consumption electric field as opposed to accelerating the cure by conventional means such as heating the material and its surrounding area or adding additional catalyst. The accelerated cure overcomes another objections to curing material in the conventional way. For example, some moldable materials give off an offensive odor as they cure. Such a material is RTV silicone rubber which gives off a pungent acetic acid odor as it sets and cures. Accelerating the cure reduces the time that these odors will be offensive to persons in the surrounding area.
Yet another advantage is that with electric field curing, the cure rate tends to be constant through the thickness of a shape. Most phase changing vehicles tend to cure more rapidly on the surface than regions in the interior of the shape. In application Ser. No. 07/589,836 entitled PROGRAMMABLE ELECTROSET MATERIALS AND PROCESSES, filed Sep. 19, 1990 (now abandoned), the disclosure of which is hereby incorporated herein by reference, the formulation and processing of electrically programmable electroset materials is taught. In an electrically programmable material as disclosed therein, end product properties of a cured material are determined by controlled electric power applied to the material during the curing phase.
In copending applications, the term electroviscous aggregate has been used to describe an aggregate which, when placed in a dielectric liquid, causes the combination of fluid and aggregate to behave electroviscously. In the present application, the term electrorheological aggregate is used in similar manner.
Electroset materials, in accordance with the present invention, comprise, castable fluid compounds such as, for example, fluid polymers and ceramics that can be caused to set and cure electrically or wherein the set and cure rate is electrically controllable. The present invention comprises electroset material that have electrically controllable end product properties. These electrically controllable end product properties include physical, structural properties, electrical properties and the end-product shape.
In my copending application Ser. No. 07/405,178 U.S. Pat. No. 5,194,181), a class of materials identified as electroset compositions was disclosed. In that application, the electroset compound was disclosed comprising a a phase changing vehicle (i.e. a castable material) and an electrorheological aggregate suitable for making the phase changing fluid electroviscous. At the time of filing the copending application Ser. No. 07/405,178, it was believed that the sole effect of applying an electric field to the electroset compound was to accelerate the cure of a compound that would otherwise cure in its normal mode of application without benefit of any specific acceleration mechanism.
It has since been determined that the physical characteristics such as for example density and specific gravity of certain electroset compounds are susceptible to influence by an applied electric field during the cure time of the material. Two part epoxy type compounds which cure by exothermic reaction are especially useful as the phase changing vehicle. Further, it has been determined that the density of the cured material may either be isotropic or anisotropic. Isotropic density means that the incremental density of the cured material remains about the same through out the volume of the cured material. Anisotropic density means that the incremental density of the cured material has readily observable different values at different parts of the volume of the cured material.
Herein the term electroshaped materials shall refer to the materials comprising any object deriving its shape, at least in part, from the application of an electric field to those materials. Thus, while it is cooling and undergoing a phase change from fluid to solid, a thermoplastic material or other phase changing vehicle with electrorheological aggregate dispersed therein can derive its shape by means of its immersion in an electric field.
Materials made in accordance with the present invention have controllably different physical end product properties. In this disclosure, the term "end product properties" refers to those properties of the material after the material has fully cured. The end product properties of the present invention can be made relatively homogenous throughout the electroset material, or alternatively, anisotropic.
The present invention is useful and advantageous in the fabrication of polymeric articles. One such article that may be advantageously manufactured using the compositions and processes of the present invention is shoe soles and portions of shoe soles. In accordance with the present invention, shoe soles are fabricated with a great variety of chosen compressibilities. Applying an electric field to properly formulated electroset material shaped in the form of a shoe sole while the electroset material is undergoing phase change from fluid to solid, will not only accelerate the cure of the sole but will alter the overall compressibility of the resultant sole. Changing the applied electric field alters the obtained compressibility of the sole. Also by selective application of field strength to various parts of the sole, the compressibility of some portions of the sole are made selectively different from other parts of the sole.
The present invention provides an advantageous means of altering the properties of a fabricated shoe sole not found in the prior art. In prior art manufacturing of castable polymer shoe soles required that the formulation of the castable polymer be changed in order to significantly change the shoe sole compressibility. Such a change in formulation requires the time consuming and messy job of recalculating the proportions of polymer constituents to be mixed, measuring out these new proportions of polymer constituent materials and then mixing. Often, the newly reformulated polymer is incompatible with the constituents of the prior polymer. This necessitates care to ensure that the prior polymer constituents and those of the new polymer are not accidently mixed together.
The materials of the present invention, on the other hand, do not need to be reformulated in order to yield changes in the desired properties of the shoe soles. Merely changing the applied electric field accomplishes this purpose. There is no need for recalculating the proportions of the polymer constituents. Furthermore, there is less likelihood in mixing constituents that should not be mixed together. Furthermore, this time consuming process is eliminated. It is taught in the co-pending applications that phase changing vehicles modified to be susceptible to the Winslow effect, can be accelerated in their cure and modified in their properties by application of an electric field during the curing phase. Electroset molds in accordance with the co-pending application are limited, however.